1. Field of the Invention
The invention relates to mass storage devices.
2. Related Art
It is often useful for mass storage, including disk drives and disk drive subsystems, to be coupled to more than one access point, such as for example more than one computer system, file server, caching device, or other system used for accessing that mass storage. For example, it is often useful for mass storage systems to be redundantly coupled to provide failover or load balancing, or to be multiply connected in the service of providing clustering, high availability, or hot swapping. Known systems for multiply coupling mass storage include SCSI (small computer systems interface) and FC-AL (fiber channel arbitrated loop). While these known systems are relatively robust in their ability to provide multiple coupling for mass storage systems, they have the drawback that they are relatively expensive and have relatively lower storage density per unit cost.
One problem with the known art is that some mass storage systems, including those mass storage devices and subsystems with the least cost and greatest storage density per unit cost, are not well-suited for being coupled to more than one controller. Examples include ATA disks, such as for example S-ATA (serial ATA) disk drives and P-ATA (parallel ATA) disk drives. Accordingly, it would be advantageous to be able to couple such mass storage systems to more than one controlling system. Moreover, it would also be advantageous to be able to use systems or techniques that are available for use with SCSI or FC-AL to provide robust multiple connectivity, with the effect of allowing such mass storage systems (for example, relatively inexpensive ATA disk drives) with systems and techniques for failover, load balancing, clustering, high availability, and hot swapping.
Accordingly, it would be advantageous to provide techniques by which disk drives having only a single controller connection might be connected to more than one controlling device.